Visually clear toothpaste compositions are well known in the art and are disclosed in many United States and foreign patents. One of the earliest patents in this field is U.S. Pat. No. 3,538,230 to Pader which discloses dentifrice compositions containing as the essential polishing and cleaning ingredient, a synthetic amorphous, porous silica xerogel. A specific example of a silica xerogel is that sold commercially under the trade name SYLOID 63 which is a preferred material in this patent and is used in commercially available toothpaste compositions. The disclosure in U.S. Pat. No. 3,538,230, also states that synthetic amorphous silicas of the prior art, such as precipitated silicas, pyrogenic silicas, and xerogels, are undesirable for dentifrice use, particularly in visually clear toothpaste compositions, either because of their initial small particle sizes or because they break down into smaller particle sizes resulting in poor cleaning ability. See U.S. Pat. No. 3,538,230, column 2, lines 12-17.
A number of U.S. patents have also been recently issued to the present applicant which disclose and claim precipitated silicas, some of which are useful as abrasive agents in toothpaste compositions, including visually clear toothpaste. These patents include U.S. Pat. No. 3,893,840, 3,928,541, 4,076,549, 4,038,098, 3,988,162, 4,015,996, 4,067,746, 3,977,893, 3,960,586, 3,967,563 and 3,993,497. Reference is also made to copending applications of the same assignee including Ser. No. 550,324, filed Feb. 18, 1975 now U.S. Pat. No. 4,105,757, Ser. No. 729,448 filed Oct. 4, 1976 now U.S. Pat. No. 4,122,160; Ser. Nos. 653,718, now abandoned, 653,719 now abandoned and Nos. 653,720, now U.S. Pat. No. 4,144,321, all filed Jan. 30, 1978; Ser. No. 854,165, filed Nov. 23, 1977; Ser. No. 876,284, filed Feb. 9, 1978 abandoned and refiled as Ser. No. 039,062, filed Aug. 11, 1979; Ser. No. 559,476, filed Mar. 18, 1975; now U.S. Pat. No. 4,122,161; Ser. No. 731,481, filed Oct. 12, 1976 now U.S. Pat. No. 4,156,717; Ser. No. 685,512, filed May 12, 1976, abandoned and refiled as Ser. No. 6,153, filed Jan. 24, 1979; Ser. No. 813,323, filed July 6, 1977 now U.S. Pat. No. 4,140,757; Ser. No. 826,901, filed Aug. 24, 1977 now U.S. Pat. No. 4,159,280; and Ser. No. 862,384, filed Dec. 20, 1977, abandoned and refiled as Ser. No. 041,952, filed Mar. 23, 1979. All of these pending applications also disclose precipitated silicas which may be used as components in toothpastes. The products of the present invention, however, have characteristics different from these prior patents and applications, which provide increased clarity. It is advantageous to the art, however, to develop new synthetic precipitated amorphous silicon dioxides which provide characteristics making them suitable for incorporation into visually clear dentifrice compositions as a substitute for the silica xerogels because the precipitated silicon dioxides are much more economical to produce and provide greater clarity than products of the prior art.